The present invention relates to a transmission control system for tractors. More particularly, the invention provides a system in which an inching or feathering clutch or clutches may be controlled as a function of engine speed.
Many modern tractor transmissions use microprocessor controlled clutches for inching or feathering. The microprocessor based Electronic Control Units (ECUs) in several tractor models manufactured by New Holland North America, Inc. utilize engine speed, output speed and brake pedal switch inputs and currently provide torque-vs-clutch pedal position control and torque-vs.-time control for inching clutch engagement as well other features. Transmissions of this type are described in U.S. Pat. Nos. 5,101,688 to Pearce et al. and U.S. Pat. No. 5,450,768 to Bulgrien et al.
An object of the present invention is to provide a novel method and apparatus for controlling clutch engagement in a transmission as a function of the speed of the engine driving the transmission.
Another object of the invention is to provide a transmission control system for a tractor or other vehicle, wherein torque transferred by a feathering clutch is controlled as a function of engine speed. This mode of control simulates operation of a centrifugal clutch but provides greater flexibility. The tractor or other vehicle may be driven using the brake pedals and a foot throttle, much like driving an automatic transmission.
A further object of the invention is to provide, in a vehicle transmission system including a transmission having an input shaft driven by an engine, an output shaft, and a clutch for controlling the transfer of torque from the input shaft to the output shaft, a method of controlling the clutch, the method comprising; sensing the speed of the engine and controlling engagement of the clutch according to the sensed engine speed whereby the transmission of torque from the input shaft to the output shaft is determined by the speed of the engine.
Yet another object of the invention is to provide a vehicle transmission system comprising: an engine driving an input shaft; an output shaft; a transmission having a clutch for transferring torque from the input shaft to the output shaft; a sensor for sensing the speed of the engine; and, a controller responsive to the sensor for controlling engagement of the clutch in response to the sensed speed of the engine, whereby the transmission of torque from the input shaft to the output shaft is determined by the speed of the engine.
The transmission system normally operates in a first mode wherein a controller is responsive to positioning of a clutch pedal to control engagement of a clutch. An auto-clutch mode may be initiated by placing the transmission in gear and depressing the vehicle brake pedals while the engine speed is less than some predetermined value. The controller compares an auto-clutch torque value to an inching clutch value and uses the smaller of these values to control clutch engagement. In the first mode, the auto clutch torque value is set to a maximum and the inching torque value is determined by the position of the clutch pedal. In the auto-clutch mode, the inching torque value is again determined by the position of the clutch pedal but the auto clutch torque value is determined by the engine speed. When operating in the auto-clutch mode, the system automatically returns to the first mode when the clutch locks up. Clutch lock up is determined by sensing the engine speed and the speed of the transmission output shaft, computing the ratio of the two speeds, and comparing the computed ratio with a stored theoretical transmission ratio.
Other objects and advantages of the invention will become apparent upon consideration of the following description and the accompanying drawings.
FIG. 1 is a schematic block diagram of a transmission control system according to the invention.
FIG. 2A shows a microprocessor-controlled powershift transmission with which the present invention may be utilized.
FIG. 2B shows the electro-hydraulic controls for the powershift clutches.
FIG. 3 is an electrical diagram illustrating certain inputs to the transmission controller.
FIGS. 4A and 4B comprise a flow diagram illustrating the steps of a routine executed by the controller to implement the auto-clutch control feature.
FIG. 5 is a graph illustrating engine speed versus percent of maximum torque available from the engine transferred through a feathering clutch.